After months of intense — and often negative — campaigning between President Barack Obama and his Republican opponent, former Massachusetts Gov. Mitt Romney, voters headed to polls across the country on Tuesday to render their verdict in America's presidential election.

The election would settle the question of which man would lead the United States for the next four years, but a great deal of uncertainty awaited the winner of the election. Either Obama or Romney will almost immediately have to face the so-called “fiscal cliff,” the cocktail of automatic spending cuts (especially to defense) and tax hikes set to take effect at the beginning of the year unless Congress acts.

Those challenges, the prospect of a “grand bargain” to address mounting national debt, and a variety of other issues confronted both the candidates and the tens of millions of voters expected to cast ballots on Tuesday.

But both campaigns fought hard for months for the right to face those challenges.

President Obama and Mitt Romney's travel schedules reveal the states that would help them attain the necessary amount of electoral votes to take the White House. NBC's Chuck Todd reports.

The dominant issue of the election was the economy — specifically whether Obama had done enough in four years to improve upon the profound recession that had just begun to take hold in the closing weeks of his 2008 campaign.

Romney argued that his business acumen uniquely qualified him as an alternative to the president, an assertion which Obama and his supporters challenged throughout the campaign.

The election played out in recent months amid green shoots of economic recovery; the U.S. added almost 1.6 million jobs so far during the 2012 calendar year, according to the Bureau of Labor Statistics.

Still, Republicans, led by Romney, argued that this wasn't enough, pointing toward the far rosier projections of recovery issued in the early days of the Obama administration.

The question of whether Obama had earned a second term, or if Romney was a sufficiently competent replacement, played out across a handful of battleground states that will decide the election's outcome.

Some of those states — Iowa, New Hampshire, Florida and Ohio — were familiar battlegrounds that have swung between Democratic and Republican candidates in recent presidential elections.

Pollsters divide the state of Ohio into five regions: coal country, northeastern Ohio, the auto belt, the Columbus area and the Cincinnati region. Currently, Obama is doing well in the north and has also made inroads in coal country – but the real area to watch is the auto belt where Romney will return to campaign Tuesday. NBC's Chuck Todd reports.

Other swing states reflected slow changes in political demographics; Obama has put states like Virginia, North Carolina, Colorado, and Nevada into play partially due to changes in those states' populations.

Romney, meanwhile, pressed the GOP cause in Wisconsin, a more reliably Democratic state in national elections that has emerged as an unlikely hotbed for a new generation of reform-minded, conservative politicians (including Romney's running mate, Rep. Paul Ryan).

Both Romney and the president spent much of the final few days making multiple stops in those few battleground states, repeating a refined and practiced speech to crowds numbering in the thousands — sometimes the tens of thousands.

Obama's schedule for the final day took him to Wisconsin, Ohio and Iowa – the states comprising his Midwestern "firewall," which his campaign hopes will insulate the incumbent against GOP victories in other battleground states.

"We've made real progress, Ohio, but the reason why we're here is because we've got more work to do," the president told a crowd in Columbus on Monday.

The President traveled more than 1000 miles Monday, visiting the three Midwestern battleground states critical to his re-election. NBC's Kristen Welker reports from Des Moines, Iowa.

"Our fight goes on because America always does best when everybody gets a fair shot and everybody does their fair share and everybody plays by the same rules. That's what we believe. That's why you elected me in 2008. And that's why I'm running for a second term for president of the United States."

Romney's last day on the campaign trail featured stops in arguably the three most critical battleground states: Ohio, Virginia, and Florida.

He wrapped the day with a rally in New Hampshire, the state which served as the cornerstone for Romney's bid for the GOP presidential nomination earlier this year and which neighbors Massachusetts, where he served as governor and where his campaign is headquartered.

Telling crowds in Florida that 'this nation is going to change for the better tomorrow,' GOP presidential candidate Mitt Romney rallied voters by saying he would break the gridlock in Washington. NBC's Peter Alexander reports from Columbus, Ohio.

Romney has leaned upon his experience as governor – and, before that, as a venture capitalist – to make the case as to why voters should expel Obama and elect him instead.

“The president promised change but he just couldn't deliver it,” Romney told a crowd in northern Virginia on Monday. “I not only promise change, I have a record of achieving it.”

Many voters were set to endure a time-honored tradition – waiting in long lines – on Election Day, though the portrait of the electorate tomorrow might not tell the full story of the 2012 election.

Many voters, encouraged by both the Obama and Romney campaigns, have cast their ballot prior to Nov. 6. Thirty percent of voters said in this weekend’s NBC News/Wall Street Journal poll that they had already cast a ballot, a proportion that could be even higher in battleground states.

Polls often show that Obama leads Romney among early voters, meaning that the Republican nominee must perform better among voters who actually head to the polls Tuesday.

The president’s campaign has also sought to take advantage of changing demographics throughout the campaign, a strategy that could pay dividends. Obama has courted young voters and gay and lesbian voters, but especially Latino and women voters.

Analysts are predicting that the new Senate may be even more narrowly divided than it is now. NBC's Kelly O'Donnell reports.

The president has made a point of assailing Romney’s approach to contraception and abortion rights and his campaign has sought to link the Republican nominee to remarks about rape by several Republican Senate candidates. Obama led Romney, 51 percent to 43 percent, among women in the final NBC/WSJ poll.

Obama also seized upon Romney’s hard-charging rhetoric toward illegal immigrants during the primary, and announced new regulations over the summer ceasing efforts to deport undocumented citizens who were brought to the U.S. as children.

The unifying issue among all those voters, however, was most certainly the economy.

Romney entered Election Day with an advantage over Obama on the raw question of which candidate voters said was better prepared to create jobs and boost the economy; 47 percent of voters in the final NBC/WSJ voters said that candidate was Romney, versus 42 percent who said that for the president.

But Obama also leads Romney by 11 percentage points on the question of which candidate better looks out for the middle class. Fifty-two percent of likely voters also said they thought the economy was improving, a sign that the U.S. has finally begun to climb out from the depths of the recession.

NBC's Tom Brokaw speaks with young voters grappling with a distrust of the political system.

But as the hours on campaign 2012 ticked down, Obama seemed on Saturday night to acknowledge a hard truth: much of his and Romney’s fates were out of their hands at this point, left to voters who would ultimately have their say on Tuesday.

“We’re props,” Obama recounted telling a top adviser during his campaign travels that day. “Because what’s happened is that now the campaign falls on these 25-year-old kids who are out there knocking on doors, making phone calls, and then we realized, you know, pretty soon after they do their jobs then they’re not relevant either because it’s now up to you.”